Surge arresters type 2 or SPD (surge protection devices) are installed in power distribution networks to protect people, systems, and equipment against impermissible, short, pulsed overvoltages. They can be used in network systems between L-N and L-PEN. Defect indication is shown by a red signal in the viewing window. Status feedback is provided as a potential-free changeover contact via a plug in the accessory pack.